diff --git a/src/bsdfs/composite.cpp b/src/bsdfs/composite.cpp
index a3ebef44..f33171d1 100644
--- a/src/bsdfs/composite.cpp
+++ b/src/bsdfs/composite.cpp
@@ -264,6 +264,8 @@ public:
 		return oss.str();
 	}
 
+	Shader *createShader(Renderer *renderer) const;
+
 	MTS_DECLARE_CLASS()
 private:
 	int m_bsdfCount;
@@ -273,6 +275,107 @@ private:
 	DiscretePDF m_pdf;
 };
 
+// ================ Hardware shader implementation ================ 
+
+class CompositeShader : public Shader {
+public:
+	CompositeShader(Renderer *renderer, const std::vector<BSDF *> &bsdfs, Float *weights) 
+		: Shader(renderer, EBSDFShader), m_bsdfs(bsdfs), m_weights(weights), m_complete(false) {
+		m_bsdfShader.resize(bsdfs.size());
+		for (size_t i=0; i<bsdfs.size(); ++i) {
+			ref<Shader> shader = renderer->registerShaderForResource(bsdfs[i]);
+			if (shader) {
+				shader->incRef();
+				/* At least one shader has a hardware implementation */
+				m_complete = true;
+			}
+			m_bsdfShader[i] = shader;
+		}
+	}
+
+	bool isComplete() const {
+		return m_complete;
+	}
+
+	void cleanup(Renderer *renderer) {
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			renderer->unregisterShaderForResource(m_bsdfs[i]);
+			if (m_bsdfShader[i])
+				m_bsdfShader[i]->decRef();
+		}
+		m_bsdfShader.clear();
+	}
+
+	void putDependencies(std::vector<Shader *> &deps) {
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			if (m_bsdfShader[i])
+				deps.push_back(m_bsdfShader[i]);
+		}
+	}
+
+	void generateCode(std::ostringstream &oss,
+			const std::string &evalName,
+			const std::vector<std::string> &depNames) const {
+		Assert(m_complete);
+		int ctr = 0;
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			if (!m_bsdfShader[i])
+				continue;
+			oss << "uniform float " << evalName << "_weight_" << ctr++ << ";" << endl;
+		}
+		oss << endl;
+		oss << "vec3 " << evalName << "(vec2 uv, vec3 wi, vec3 wo) {" << endl
+			<< "    return ";
+		ctr = 0;
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			if (!m_bsdfShader[i])
+				continue;
+			oss << endl << "      ";
+			if (ctr != 0)
+				oss << "+ ";
+			else
+				oss << "  ";
+			oss << depNames[ctr] << "(uv, wi, wo) * "
+							  << evalName << "_weight_" << ctr;
+			ctr++;
+		}
+		oss << ";" << endl;
+		oss << "}" << endl;
+	}
+
+	void resolve(const GPUProgram *program, const std::string &evalName, std::vector<int> &parameterIDs) const {
+		int ctr = 0;
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			if (!m_bsdfShader[i])
+				continue;
+			parameterIDs.push_back(
+				program->getParameterID(formatString("%s_weight_%i", evalName.c_str(), ctr++)));
+		}
+	}
+
+	void bind(GPUProgram *program, const std::vector<int> &parameterIDs, int &textureUnitOffset) const {
+		int ctr = 0;
+		for (size_t i=0; i<m_bsdfs.size(); ++i) {
+			if (!m_bsdfShader[i])
+				continue;
+			program->setParameter(parameterIDs[ctr++], m_weights[i]);
+		}
+	}
+
+
+	MTS_DECLARE_CLASS()
+private:
+	std::vector<Shader *> m_bsdfShader;
+	const std::vector<BSDF *> &m_bsdfs;
+	const Float *m_weights;
+	bool m_complete;
+};
+
+Shader *Composite::createShader(Renderer *renderer) const { 
+	return new CompositeShader(renderer, m_bsdfs, m_bsdfWeight);
+}
+
+MTS_IMPLEMENT_CLASS(CompositeShader, false, Shader)
 MTS_IMPLEMENT_CLASS_S(Composite, false, BSDF)
-MTS_EXPORT_PLUGIN(Composite, "Composite BRDF");
+MTS_EXPORT_PLUGIN(Composite, "Composite BRDF")
 MTS_NAMESPACE_END
diff --git a/src/bsdfs/lambertian.cpp b/src/bsdfs/lambertian.cpp
index 7df91f92..e8db43b6 100644
--- a/src/bsdfs/lambertian.cpp
+++ b/src/bsdfs/lambertian.cpp
@@ -146,5 +146,5 @@ Shader *Lambertian::createShader(Renderer *renderer) const {
 
 MTS_IMPLEMENT_CLASS(LambertianShader, false, Shader)
 MTS_IMPLEMENT_CLASS_S(Lambertian, false, BSDF)
-MTS_EXPORT_PLUGIN(Lambertian, "Lambertian BRDF");
+MTS_EXPORT_PLUGIN(Lambertian, "Lambertian BRDF")
 MTS_NAMESPACE_END
diff --git a/src/libhw/renderer.cpp b/src/libhw/renderer.cpp
index 5a982df1..703ed98c 100644
--- a/src/libhw/renderer.cpp
+++ b/src/libhw/renderer.cpp
@@ -67,6 +67,8 @@ Shader *Renderer::getShaderForResource(const HWResource *resource) {
 }
 
 void Renderer::unregisterShaderForResource(const HWResource *resource) {
+	if (resource == NULL)
+		return;
 	if (m_shaders.find(resource) == m_shaders.end())
 		return;
 	ShaderRecord &sRec = m_shaders[resource];
diff --git a/src/librender/scene.cpp b/src/librender/scene.cpp
index 2643c98d..a283343c 100644
--- a/src/librender/scene.cpp
+++ b/src/librender/scene.cpp
@@ -243,7 +243,9 @@ void Scene::initialize() {
 	if (!m_luminairePDF.isReady()) {
 		if (m_luminaires.size() == 0) {
 			Log(EWarn, "No luminaires found -- adding a constant environment source");
-			addChild("", PluginManager::getInstance()->createObject(Luminaire::m_theClass, Properties("constant")));
+			Properties constantProps("constant");
+			constantProps.setSpectrum("intensity", Spectrum(0.5f));
+			addChild("", PluginManager::getInstance()->createObject(Luminaire::m_theClass, constantProps));
 		}
 
 		/* Calculate a discrete PDF to importance sample luminaires */
diff --git a/src/luminaires/constant.cpp b/src/luminaires/constant.cpp
index e6ce68f4..0835c0e3 100644
--- a/src/luminaires/constant.cpp
+++ b/src/luminaires/constant.cpp
@@ -27,7 +27,7 @@ public:
 	void preprocess(const Scene *scene) {
 		/* Get the scene's bounding sphere and slightly enlarge it */
 		m_bsphere = scene->getBSphere();
-		m_bsphere.radius *= 2.0f;
+		m_bsphere.radius *= 1.01f;
 		m_surfaceArea = m_bsphere.radius * m_bsphere.radius * M_PI;
 	}
 
@@ -114,7 +114,7 @@ public:
 		Float radius = m_bsphere.radius;
 		if (eRec.type == EmissionRecord::EPreview) {
 			/* This is more suitable for VPL-based rendering */
-			radius *= 10;
+			radius *= 1.5;
 		}
 		Vector d = squareToSphere(sample);
 		eRec.sRec.p = m_bsphere.center + d * radius;
@@ -126,7 +126,7 @@ public:
 	Spectrum sampleEmissionDirection(EmissionRecord &eRec, const Point2 &sample) const {
 		Float radius = m_bsphere.radius;
 		if (eRec.type == EmissionRecord::EPreview) 
-			radius *= 10;
+			radius *= 1.5f;
 		Point p2 = m_bsphere.center + squareToSphere(sample) * radius;
 		eRec.d = p2 - eRec.sRec.p;
 		Float length = eRec.d.length();
diff --git a/src/luminaires/envmap.cpp b/src/luminaires/envmap.cpp
index 81e17ab8..4f5ad876 100644
--- a/src/luminaires/envmap.cpp
+++ b/src/luminaires/envmap.cpp
@@ -195,7 +195,7 @@ public:
 		} else {
 			/* Preview mode, which is more suitable for VPL-based rendering: approximate 
 			   the infinitely far-away source with set of diffuse point sources */
-			const Float radius = m_bsphere.radius * 10;
+			const Float radius = m_bsphere.radius * 1.5f;
 			Vector d = squareToSphere(sample);
 			eRec.sRec.p = m_bsphere.center + d * radius;
 			eRec.sRec.n = Normal(-d);
@@ -207,7 +207,7 @@ public:
 	Spectrum sampleEmissionDirection(EmissionRecord &eRec, const Point2 &sample) const {
 		Float radius = m_bsphere.radius;
 		if (eRec.type == EmissionRecord::EPreview) 
-			radius *= 10;
+			radius *= 1.5f;
 		Point p2 = m_bsphere.center + squareToSphere(sample) * radius;
 		eRec.d = p2 - eRec.sRec.p;
 		Float length = eRec.d.length();